1. The Field of the Invention
The present invention relates to spin-valve sensors for reading information signals from a magnetic medium and more particularly to novel structures for spin-valve sensors and magnetic recording systems which incorporate such sensors.
2. The Relevant Art
Computer systems generally utilize auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device, such as a disk drive, incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data are recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic recording heads carrying read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, a giant magnetoresistance (GMR) head carrying a spin-valve sensor is now extensively used to read data from the tracks on the disk surfaces. This spin-valve sensor typically comprises two ferromagnetic films separated by an electrically conducting nonmagnetic film. The resistance of this spin-valve sensor varies as a function of the spin-dependent transmission of conduction electrons between the two ferromagnetic films and the accompanying spin-dependent scattering which takes place at interfaces of the ferromagnetic and nonmagnetic films.
In the spin-valve sensor, one of the ferromagnetic films, referred to as a pinned layer, typically has its magnetization pinned by exchange coupling with an antiferromagnetic film, referred to as a pinning layer.
The magnetization of the other ferromagnetic film, referred to as a xe2x80x9csensingxe2x80x9d or xe2x80x9cfreexe2x80x9d layer is not fixed, however, and is free to rotate in response to the field from the recorded magnetic medium (the signal field). In the spin-valve sensors, the GMR effect varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the sensing layer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium causes a change in the direction of magnetization in the sensing layer, which in turn causes a change in the resistance of the spin-valve sensor and a corresponding change in the sensed voltage.
FIG. 1 shows a typical prior art spin-valve sensor 100 comprising a pair of end regions 103 and 105 separated by a central region 102. The central region 102 is formed by depositing various layers onto a bottom gap layer 118, which is previously deposited on a bottom shield layer 120, which is, in turn, deposited on a substrate. Two end regions 103, 105 abut the edges of the central region 102. A ferromagnetic sensing layer 106 is separated from a ferromagnetic pinned layer 108 by an electrically conducting nonmagnetic spacer layer 110. The magnetization of the pinned layer 108 is fixed through exchange coupling with an antiferromagnetic pinning layer 114. This spin-valve sensor is sputtered onto seed layers 116, on which the pinning, pinned, spacer and sensing layers of the spin-valve sensor grow with preferred crystalline textures during sputtering so that desired improved GMR properties are attained.
The end regions 103 and 105 are also formed by a suitable deposition method such as sputtering of various layers onto the bottom gap layer 118. Longitudinal bias (LB) and conducting lead layers 126 abut the spin-valve sensor. The central and end regions are sandwiched between electrically insulating nonmagmetic films, one referred as a bottom gap layer 118 and the other referred as a top gap layer 124.
The disk drive industry has been engaged in an ongoing effort to increase the recording density of hard disk drives, and correspondingly to increase the overall signal sensitivity to permit the GMR head of the hard disk drives to read smaller changes in magnetic flux. The major property relevant to the signal sensitivity of a spin-valve sensor is its GMR coefficient. A higher GMR coefficients leads to higher signal sensitivity and enables the storage of more bits of information on a disk surface of a given size. The GMR coefficient of the spin-valve sensor is expressed as xcex94RG/Rll where Rll is a resistance measured when magnetizations of the free and pinned layers are parallel to each other, and ARG is the maximum giant magnetoresistance (GMR) measured when magnetizations of the free and pinned layers are antiparallel to each other.
Other properties relevant to the signal sensitivity of the spin-valve sensor include exchange coupling between the antiferromagnetic pinning and ferromagnetic pinned layers. This exchange coupling must be high in order to keep the magnetization of the pinned layer at a direction perpendicular to an air bearing surface for optimal sensor operation. An inadequate exchange coupling may cause canting of the magnetization of the pinned layer from the preferred direction, thereby reducing the signal sensitivity of the spin-valve sensor.
It is also vital that the sensing current flowing in the spin-valve sensor be confined to the pinned 108, spacer 110 and sensing 106 layers of the spin-valve sensor. If the sensing current is permitted to shunt through the pinning 114 or other layers, the resistance of the spin-valve sensor will be low, thus producing a low GMR coefficient. Accordingly, the material selected for the pinning layer must possess a high electrical resistivity in order to prevent the current shunting.
In certain spin-valve sensors, particularly those with a Ni-Fe sensing layer, a cap layer 112 is often formed over the sensing layer. The cap layer 112 serves several purposes, and plays a crucial role in attaining a high GMR coefficient. For instance, a Cu cap layers is thought to induce spin filtering, while a NiO cap layer is thought to induce specular scattering. Both spin filtering and specular scattering are believed to increase the GMR coefficient of a spin-valve sensor. In addition, a cap layer may be employed to prevent the underlying sensing layer from interface mixing occurring immediately during depositions and oxygen diffusion occurring during subsequent annealing, thereby maintaining suitably soft magnetic properties of the sensing layer and improving the thermal stability of the spin-valve sensor. The term xe2x80x9csoft magnetic propertyxe2x80x9d refers to the capability of a spin-valve sensor to sense very small magnetic fields.
Currently, a Ta cap layer is used in many conventional spin-valve sensors. However, the Ta cap layer does not exhibit desired specular scattering, and is considered inadequate in preventing the sensing layer from interface mixing and oxygen diffusion. Interface mixing originates from direct contact between the sensing layer and the Ta cap layers, and causes a substantial loss in the magnetic moment of the sensing layer. For one currently used spin-valve sensor with a 0.32 memu/cm2 sensing layer, this magnetic moment loss accounts for 25% of the magnetic moment of the sensing layer. Oxygen diffusion originates from low passivity of the Ta cap layer, which oxidizes continuously and entirely during annealing, such that oxygen eventually penetrates into the sensing layer, causing more losses in the magnetic moment of the sensing layer.
Thus, it can be seen from the above discussion that there is a need existing in the art for an improved spin-valve sensor with an increased GMR coefficient and improved thermal stability. Particularly, it would be advantageous to provide a spin-valve sensor with a suitable cap layer to achieve the increased GMR coefficient and improved thermal stability through decreases in the occurrence of interface mixing and oxygen diffusion.
The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available spin-valve sensors. Accordingly, it is an overall object of the present invention to provide an improved spin-valve sensor that overcomes many or all of the above-discussed shortcomings in the art.
To achieve the foregoing object, and in accordance with the invention as embodied and broadly described herein in the preferred embodiments, an improved spin-valve sensor is provided and configured with a cap layer formed by deposition and in-situ oxidation in a controlled environment. Top and bottom gap layers may also be formed using the deposition/in-situ oxidation method of the present invention. A method of the present invention is also presented for forming an in-situ oxidized metal film on a spin-valve sensor with a deposition/in-situ oxidation process.
The spin-valve sensor of the present invention is preferably incorporated within a disk drive system configured substantially in the manner described above. In addition, the spin-valve sensor of the present invention preferably comprises a cap layer formed of an in-situ oxidized metal film. In one embodiment, the film is Al, Hf, Si, Y, or Zr. In alternate embodiments of the invention, a noble metallic film, e.g., Au, Cu, Rh, or Ru may be sandwiched between the sensing layer and the in-situ oxidized cap layer.
The spin-valve sensor preferably comprises one or more seed layers, a pinning layer, a pinned layer, a spacer layer, a sensing layer, and a cap layer, as discussed above. Nevertheless, the in-situ oxidized cap layer of the present invention is intended for use with any type of spin-valve sensor having a suitable construction.
In one embodiment, a bottom shield layer preferably formed of a Ni-Fe film and a bottom gap layer preferably formed of an Al2O3 film are deposited on a wafer. Multiple seed layers preferably formed of Al2O3, Ni-Cr-Fe and Ni-Fe films are deposited on the bottom gap layer. A pinning layer preferably formed of a Pt-Mn film is then deposited on the multiple seed layers. Pinned layers preferably formed of Co-Fe, Ru and Co-Fe films are then deposited on the pinning layer. A spacer layer preferably formed of an oxygen-doped, in-situ oxidized Cu-O film is then deposited on the pinned layer. Sensing layers preferably formed of Co-Fe and Ni-Fe films are then deposited on the spacer layer. A cap layer preferably formed of an in-situ oxidized Al film (Al-O) is then formed on the sensing layer with a deposition/in-situ oxidization process. Partial in-situ oxidization is preferred for attaining a high GMR coefficient.
In an alternative embodiment, top and bottom gap layers preferably formed of multilayer in-situ oxidized Al films are formed on the wafer. The deposition/in-situ oxidation process is repeated until selected thicknesses of the top and bottom gap layers are attained. Full in-situ oxidization of the top and bottom gap layers is preferred for attaining high breakdown voltages.
The deposition/in-situ oxidation process preferably comprises depositing a metal film in a deposition chamber in a vacuum without the presence of oxygen, and then conducting the in-situ oxidization for a wide range of time in a wide range of oxygen pressures in an oxidation chamber. The wafer is then transferred to a second chamber where the metal is naturally oxidized. In one embodiment given by way of example, the in-situ oxidization is conducted for a period of about 8 minutes in about 0.5 Torr of oxygen. The exposure to oxygen is preferably conducted with a moderate temperature, such as ambient room temperature.
The top and bottom gap layer may likewise be deposited using the deposition/in-situ oxidization process of the present invention. In order to achieve greater thicknesses of these layers, multiple layers may be alternatively deposited and oxidized using the deposition/in-situ oxidation process. Preferably, when forming the seed and gap layers, the alternating oxidized layers are fully oxidized.
These and other objects, features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.